Pumping viscous crude



Sept. 16, 1969 c, MCAULIFFE ETAL 3,467,195

PUMPING VISCOUS CRUDE Filed April 25, 1968 22 J v I l I I SURFACTANT BNVENTORS CLAYTON D. McAUL/FFE RALPH S/MON CARL E. JOHNSON, JR.

AVTORNE United States Patent Oflice 3,467,195 Patented Sept. 16, 1969 3,467,195 PUMPING VISCOUS CRUDE Clayton D. McAulilfe, Fullerton, Ralph Simon, Whittier,

and Carl E. Johnson, Jr., Laguna Beach, 'Calif., assignors to Chevron Research Company, San Francisco, Calif., a corporation of Delaware Continuation-impart of application Ser. No. 642,284, May 18, 1967. This application Apr. 25, 1968, Ser. No. 724,194

Int. Cl. E21b 43/00; C09k 3/.00

US. Cl. 166-314 6 Claims ABSTRACT OF THE DISCLOSURE The invention is directed to improving the pumpability of crude oil from a well by injecting predeterminable amounts of nonionic surfactant into the well to contact oil and water to form a low viscosity oil-in-water emulsion near the pump in the well.

This application is a continuation-in-part of Ser. No. 642,284, filed May 18, 1967, now US. Patent No. 3,380,- 531, issued Apr. 30, 1968, which in turn, is a continuation-in-part of Ser. No. 503,210, filed Oct. 23, 1965, and now abandoned.

The present invention relates to a method of pumping viscous crude oil. More particularly, it relates to a method of pumping viscous crude by contacting the viscous oil with predetermined amounts of nonionic surfactant in the presence of water to form an oil-in-water emulsion of said crude at a point adjacent the actuating element of a downhole pump and then pumping said emulsion having a substantially lower viscosity than the native oil from the well.

Viscosity frequently limits the rate crude oil can be produced from a well. For example, in wells that are pumped by a sucker rod string, viscous drag by the crude oil on the string slows its free fall by gravity on the downstroke. On the upstroke, this drag also slows the string, decreases oil flow through the production tubing, and increases the power required to raise oil and rod string. In some instances where the oil is highly viscous, such as the Boscan Field in Venezuela, the strength of the sucker rods limits the depth at which the pump can be operated. Alternatively, hydraulic pumps can be placed at the bottom of the well, but they must still overcome the high viscous drag that requires high power oil pressures and high pump horsepower.

The downhole pump usually provides the pressure required to pump the produced oil from the wellhead to surface gathering tanks. Where viscosity is high, this may require the use of extra strength wellhead equipment (packings, gaskets, heavy walled pipes and the like) to withstand the pressures required to move such viscous oil from wellhead to storage tank.

It has been proposed heretofore to reduce the viscosity of heavy crude oils prior to pumping by introducing low viscosity crude oils, white oil, kerosene or the like into the well bore to dilute or thin the produced crude. In rod pumped wells, it is common to surround the sucker rod string with an extra tubing. Low viscosity oil is pumped down this tubing so that the string is surrounded by lower viscosity oil. This added light oil then mixes with the viscous crude near the traveling valve of the pump to lighten and thin the column of crude oil being pumped from the well through the annulus formed by the inner and the production tubings of the well. Alternatively, low viscosity oil can be pumped down hollow sucker rods and the diluted crude oil produced through the annular between the hollow rod string and the tubing.

As noted above, wells are also frequently pumped by downhole hydraulic units. In these wells a low viscosity oil is used as a power fluid. Frequently it is also mixed with the crude under production. In such a system it is common to reclaim the lower viscosity or high gravity components from the mixed, produced fluid for reuse as the power oil. However, in some wells the native crude contains so little low viscosity components that it is necessary to import oil from other sources for use as the power fluid. Economically, this may make it necessary to use a closed hydraulic system. To operate as a closed system, the downhole hydraulic pump is connected to the surface by two pipes to supply and return the power oil and thereby prevent it from comingling with the crude. Obviously, the viscosity of the produced crude is not reduced by the power oil and great hydraulic power is required to lift the crude.

None of the above described systems greatly reduces the viscosity of the native crude oil, unless excessive volumes of the high gravity fluids are used. Furthermore, it is expensive to reclaim the less viscous oil added to the produced crude,

In accordance with the present invention, it is a primary object to reduce the power required to pump high viscosity crude down to values that are substantially the same as that required to pump water, and at the same time, reduce the cost of extracting the viscous crude oil from the produced fluid on stream.

Briefly, the invention has to do with a process of increasing the pumpability of a viscous crude pumped from a well bore by means of a downhole pump in said well bore, which comprises injecting predeterminable amounts of nonionic surfactant into the well to contact oil in the presence of water to form an oil-in-water emulsion of the viscous crude, said emulsion having a substantially lower viscosity than the unemulsified crude, and pumping the oil-in-water emulsion to the surface of the ground.

In one aspect, the invention provides a method of improving the pumpability of crude from a well by forming an oil-in-water emulsion in the well by mixing with the oil an aqueous soluton containing a nonionic surfactant. In many instances it is possible to utilize the connate water already present in the well and form the oil-inwater emulsion by injecting a nonionic surfactant down the well. The oil-in-water emulsion which is formed by mixing the nonionic surfactant solution and the oil in a well adjacent a downhole pump s relatively stable while the mixture is being moved. The mixture tends to separate into a separate oil phase and a separate water phase when left standing and therefore the mixture can be easily broken down into separate oil and water phases. The oilin-water emulsion may be formed with as little as 15% water containing the surfactant solution. It is preferred, however, to have substantially more water containing surfactant solution present in the well when forming the emulsion. A 50/50 ratio of surfactant solution is added to the oil to form the desired mixture. As indicated, the amount of water may be as little as about 15%. The surfactant is added to the water before the water is mixed with the oil. In accordance with the invention, from .02 to .4 pound of surfactant per barrel of oil produced from the well is added to oil and water to form the oil-inwater emulsion adjacent the downhole pump. It is preferred to add about .1 pound of surfactant per barrel of oil produced from the well.

Nonionic surfactants useful in the present invention can be divided into five basic types by linkage. (See Emulsion Theory and Practice, by P. Becher, ACS Monograph, No. 162, 1965, Reinhold Publishers, New York.) These five types are ether linkage, ester linkage, amide linkage, miscellaneous linkage and multiple linkage.

Further objects and advantages of the present invention will become apparent from the following detailed description, including exemplification of the invention applied to viscous crude oils, taken in conjunction with the accompanying drawing which is a schematic, vertical sectional view of one form of apparatus suitable for practice of the method of this invention.

The method of the present invention is illustrated in the drawing by a rod-actuated downhole pump unit indicated generally by the number 24. The present invention permits reducing the viscosity of the pumped fluid to just about that of water. This reduction in viscosity is achieved by injecting an aqueous surfactant solution into the well to form an oil-in-water emulsion adjacent the pumping unit 24. The oil-in-water emulsion is formed as the surfactant solution and any water entering from the well meets with oil entering the well or contained in the well. The emulsion creating nonionic surfactant solution flows from tank 10 through line 14 and metering pump 16 through valve 18 into the annulus between well casing 20 and production tubing 22. The solution then proceeds down the casing annulus and intermixes with the well fluids above the pump 24 in the tubing-casing annulus indicated generally as 26.

As the emulsion is formed in the well adjacent pumping unit 24, it is pulled into the interior of the production tubing through standing valve 30 by means of the action of traveling valve or plunger 32, the details of which are well known in the art and are, therefore, not fully illustrated in the drawing. The plunger 32 is reciprocated by means of sucker rod string 34 which, in turn, is moved by surface pumping unit 36. The oil which is pumped up the production tubing 22 leaves through surface flow line 38 and suitable valve 40 to separator 42 where any free gas is removed from the emulsion. The emulsion is then flowed through line 44 to settling tank 46 from which oil and water can be separately drawn off.

Metering pump 16 supplies the surfactant solution to annulus 26 at a rate sufiicient to form with injected or formation water in the well an oil-in-water emulsion. Since most wells in which the present invention will have its greatest utility contain sufficient native or formation water to form a suitable oil-in-water emulsion upon the introduction of a nonionic surfactant, it is usually preferred to inject a relatively concentrated surfactant solution into the well from the surface. Thus the surfactant solution is preferably made up of water containing from 2% to by weight surfactant. The metering pump is adjusted to inject surfactant at a rate within the range of from .02 pound of surfactant per barrel of oil produced from the well to about .4 pound of surfactant per barrel of oil produced from the well. In most applications, a rate in the range of between .05 pound per barrel and .15 pound per barrel will be suitable. The best results in many cases are obtained when the metering pump is adjusted to inject about .1 pound of surfactant per barrel of oil produced from the well.

In accordance with the preferred form of the invention, a nonionic surfactant solution is used to form the oil-in- Water emulsion. The oil-in-water emulsion may be formed with a little as 15% water containing surfactant solution. It is preferred, however, to have substantially more water present in the well when forming the emulsion. A 50/50 ratio of water containing surfactant solution and oil has given good results. Usually most wells producing viscous crude oil also produce a great deal of water. Therefore, the surfactant can be added to the well in a concentrated form utilizing the connate water to form the emulsion.

As indicated above, the upper oil/ water ratio is limited by the amount of water needed to produce a suitable oilin-water emulsion for pumping. The upper limit for oil in most surfactant and crude oil mixtures is about 85 percent. Thus the minimum amount of water that can be used in accordance with the present invention usually is 4 about 15 It is preferred, however, to have excess water available to insure that inversion of the emulsion will not occur. Inversion of the emulsion to a water-in-oil emulsion is extremely undesirable since water-in-oil emulsions are very viscous.

It has been found that the amount of surfactant added to the well is important in insuring the success of the present method. Amounts of surfactant ranging from .02 pound of surfactant per barrel of oil produced from the well to about .4 pound of surfactant per barrel of oil produced from the well have given satisfactory results. A particularly preferred range is between .05 pound per barrel of oil and .15 pound per barrel of oil produced. The most highly satisfactory results from a performance and economics standpoint is obtained using about .1 pound of surfactantper barrel of oil produced. When the well has sufficient connate water present to form an oilin-water emulsion so that addition of water from. the surface is not necessary, it is preferred to add the surfactant in fairly concentrated liquid form. Thus a concentrated aqueous solution having enough water to maintain the surfactant in liquid form is suitable. Water containing from 2 to 5% by weight surfactant has been found to form a suitable surfactant solution for injecting into a well to emulsify the crude contained therein with connate water also present in the well.

An aqueous surfactant solution is added to the oil to form the desired mixture. As indicated, the total amount of water in the well may be as little as about 15%, although it is usually desirable to have substantially more water present to prevent inversion of the emulsion. Nonionic surfactants useful in the present invention can be divided into five basic types by linkage. (See Emulsion Theory and Practice, by P. Becher, ACS Monograph, No. 162, 1965, Reinhold Publishers, New York.) These five types are ether linkage, ester linkage, amide linkage, miscellaneous linkage and multiple linkage. The ether linkage, nonionic surfactants are preferred for use in the present invention. The surfactants preferred for use in the present invention are selected from the group having the general formulas:

where R, R and R any hydrocarbon group and 11 and n 4 to 100.

As indicated above, other surfactants, such as the ester linkage and the amide linkage, may be used in accordance with the invention. The general formula for the ester linkage is:

H rt-o-o-wrncrnomr where R any hydrocarbon group and n 4 to 100. The general formula for the amide linkage surfactant where R any hydrocarbon group and 11 and n 4 to 100.

The highly preferred nonionic surfactants for use in accordance with the invention are the nonylphenoxypoly (ethyleneoxy)ethanols. Superior results have been obtained with surfactants containing 10-15 moles ethylene oxide per mole of nonylphenol. These surfactants have decreasing water solubility with increasing temperature. Emulsions up to 70% oil formed with these types of surfactants have good stability up to 160 F. and fair stability in the 160-175 F. range. At temperatures in the 200 F. range, separation of oil and water is rapid, and gravity separation can produce a low water cut oil. Surfactants operable at higher temperatures are also available.

The highly preferred surfactants are selected from a group having the general formulas:

R- '"O (OH2CHQO)IJH and 0(0Hg0Hq0)nH R.

where R, R and R any alkyl radical and where n 4 to 100.

A list of highly preferred surfactants is set out below:

2-4 dinonyl. B Proprietary mixture, chemically similar to Igepal 0 0-887.

Suitable ester linkage surfactants, for example, include surfactants having the following formulas:

and

Table II sets out the results of a number of demonstrations showing various combinations of oil/water ratios, surfactants, and surfactant percentages useful in forming transportable emulsions in accordance with this invention. The results show that suitable mixtures may be formed with water containing .05 surfactant based on added water. It is usually preferred, however, to form the mixture with at least about .l% surfactant based on added water. The advantage that is obtained by forming the transportable mixture is readily seen in the case of Boscan crude. The viscosity of pure Boscan crude is 80,000 centipoises at 70 F. However, the viscosity of an emulsion containing 75% Boscan and 25% water is only centipoises at 70 F. Table II shows properties of various mixtures of Boscan crude, water and surfactants.

TABLE 11 Chemical Water remaining Vol. Mixture in oil percent Viscosity separated in at 200 F., Separation Name water F. 0p. percent time, hours 00-710 0. 10 117 93 11. 7 4 00-710 0. 10 112 78 2. 0 3 011-630 0. 10 116 10. 8 2 0A-630 0. 10 108 67 2. 0 3 DM-970 0. 10 121 12. 5 1 DM-970 0. 10 108 69 2. 4 6 DME 0. 10 109 91 10. 5 3 DME 0. 10 104 3. 9 5 N IW 0. 10 120 59 NIW 0. 10 122 56 10. 6 6 NIW 0. 10 116 46 2. 1 8 N IW 0. 10 127 49 N IW 0. 10 120 48 10. 0 2 N IW 0. 05 118 11 N IW 0. 05 120 43 10. 3 3 N IW O. 05 123 26 11. 0 75 N IW 0. 05 00-710 0. 10 123 97 10. 2 2. 5 00-730 0. 10 92 8. 6 3. 5 00-730 0. 10 116 147 8. 0 4. 5 00-850 0. 10 110 142 11. 9 22 00-850 0. 10 111 187 12. 0 6 00-887 0. 10 112 102 12. 0 2. 5 00-88? 0.10 117 188 11. 0 2. 5 0 O-436 0. 10 103 104 8. 7 1 00-436 0. 10 117 149 11. 6 3 011-630 0. 10 110 48 8, 0 5 DM-710 0. 10 64 9. 0 3 DM-710 0. 10 120 55 10. 5 2 DM-970 0. 10 116 93 9. 7 2 DME 0. 10 114 159 11. 0 5 N IW 0. 15 116 68 11. 0 6 NIW 0. 20 117 72 15. 0 6 Visco 1111 0. 20 114 Viseo 1111 0.30 106 IVlSco 1111 0. 05} 108 \N IW 0. 05 a1 75/25 {8822 6 8; 82} 110 Visco 1111 0. 05 38 75/25 {00-850 0. 05} 114 The advantages of the method of the present invention have been demonstrated with a number of other crude oils. Table III sets out the properties of mixtures prepared with California crude oils utilizing fresh water and various surfactants. The California crude oils are namely indicated at A, B and C. The A crude has an API gravity of 12.17 and a viscosity of 14,000 centipoises at 70 F. The B crude has an API gravity of 12.17 and a viscosity of 19,000 centipoises at 70 F. The C crude has an API gravity of 10.15 and a viscosity of 70,000 centipoises at 70 F.

TABLE III Chemical concentration in Emulsion viscosity water, volume percent Temperature, Viscosity, Chemical F. cp.

NIW

Zone

TABLE IV Chemical tration in water, volume Viscosity, percent F. cp.

Emulsion viscosity Water Produced d Zone PPPPPPQPPp O H CO meeoeeawss As is evident from the data presented in Tables II, III and IV, a tremendous improvement in viscosity can be obtained by forming transportable emulsions of the viscous crudes in accordance with the present invention.

Table V below shows the effect of gradually decreasing the water content in the aqueous surfactant mixture. The crude oil used in Table V was a California crude type A oil maintained at 140 F. A 0.1% Igepal CO-850 in tap water at 72 F. formed the aqueous solution. It is apparent that oil-in-Water emulsions were formed at the 75/25 to the 85/15 mixtures because the mixtures were water wet and had electrical conductivity.

TABLE V Dispersed in Water Elect.

glass conductivity Wall Toluene The data given in Tables V and VI indicate that the upper limit for oil in most aqueous solution, crude oil mixtures is about 85% in order to form a suitable mixture for pumping.

It has been found that the Water with which the mixtures of the present invention are formed is not limited to distilled or potable water. The nonionic surfactants are not affected by salts in solution in the water; and, therefore, formation water, and even seawater, can be used in forming the mixtures in accordance with the present invention. This is a particularly desirable feature in field operations since it may not be economical to obtain large quantities of relatively fresh Water for use in the process or the connate Water in the well may have high salt content. Table VII sets out the properties of a Boscan crude, aqueous surfactant mixture when the water utilized was seawater. Two emulsions were prepared with different surfactants and with seawater obtained directly from the ocean at Huntington Beach, Calif.

In a field test conducted to show the advantages of this aspect of the present invention, a nonionic surfactant was added to a producing well in the Huntington Beach Field in California. The nonionic surfactant was Igepal CO- 850 and has the general formula:

where R=C H and 11:20.

The well originally was producing 13 barrels of oil and 15 barrels of Water per day. The well was completed in three producing zones with the operating fluid level covering only the bottom zone. The nonionic surfactant was added to the annulus between a producing string and the casing. The surfactant was mixed with water at the surface for injection in the annulus. One-tenth of a pound of surfactant per barrel of oil produced was added to the well. Thus, when the Well was producing 13 barrels of oil per day, 1.3 pounds of surfactant was used. This daily amount of surfactant was mixed with from 2 /2 to 5 barrels of water for daily injection. The surfactant solution was metered into the well over a 24 hour period. As indicated above, the oil production without surfactant was 13 barrels of oil per day and 15 barrels of water. With the surfactant added to the well, 14 barrels of oil per day and 20 barrels of water per day were produced. The major improvement, however, occurred in improving the efiiciency with which the oil was produced. For example, the pressure drop in the 900 feet of 2 /2 inch tubing in the well was 800 p.s.i. before the surfactant was added. The pressure drop in the line after the addition of surfactant, was reduced to only p.s.i. The polished rod horsepower prior to the addition of surfactant was 3 horsepower and after the addition of surfactant was only 2 horsepower. The peak torque prior to the addition of surfactant was 55,000 inch/pounds and with surfactant, was

reduced to 30,000 inch/pounds. Downhole pump efliciency Without surfactant was 47% and with surfactant was 60%. In addition, the use of surfactant caused the fluid level over the pump to be reduced from 600 feet to 300 feet. The surfactant also had a marked effect on the process of rod drop. The frictional drag on the pump rod during downstroke was reduced to /6 the original drag by the use of surfactant. The above figures indicate that wells utilizing the method of the present invention can be handled with smaller pumping units and lighter rod strings. It is also expected that oil recovery will be improved due to the lowering of the fluid level in the well.

A second field test was conducted in the Kern River Field. The test involved nonionic surfactant injection in four wells whose production had been curtailed by slow rod drop and extended periods of downtime due to pumping unit difliculties. During a six-month test period, rod drop rate in the four wells was improved substantially, and the three wells for which production history was available produced approximately 1700 barrels of additional oil (a 34% increase) over the 5000 barrel production estimated for the same period without emulsification.

Two 55 gallon drums and a small gas-operated chemical pump were installed at each of three wells on the Kosanke lease, Kern River Field, to continuously inject an aqueous solution of nonionic surfactant Igepal DM- 710 into the casing-tubing annulus. The injection equipment was similar to that shown in the drawing. DM710 was selected for the field test because it was the best of a series of nonionic surfactants tested in the laboratory. Each injection pump had a capacity of about gal/day, and each pair of 55 gallon drums provided five days surfactant solution supply. Treatment was started by dumping 50 barrels of water containing 0.2 volume percent DM-710 into the annulus of each well. The wells were then circulated about two hours to form a water film on the casing, tubing, and rods and to form a low viscosity O/W emulsion in the well. A visible rod drop improvement was observed while the wells were being circulated. After the circulation period, the wells were turned into the flow lines, and the continuous surfactant injection pumps started. Surfactant injection was initially set at 0.4 lb./bbl. of total oil produced and later reduced to about 0.15 lb./bbl. It is believed that about 0.08 lb./bbl. of total oil produced would be helpful in giving effective results. In addition to the continuous treatment test in the three Kosanke wells, a successful batch treatment was conducted in one well on an adjacent lease in the Kern River Field. Discussion of the specific wells is given below.

Kosanke well 86B normally produces 10% oil and 90% Water. The oil is about 11 API and has a viscosity of 42,000 centipoises at 80 F., the average flow line temperature. This well could not be produced for a twomonth period before the test because the pumping unit could not be balanced with the extremely slow rod fall rate. Hot water batch treatments were ineffective, and Without downhole emulsification it would have been necessary to resteam the well earlier than normal to return it to production. The well had been steamed about a year before the present field test and oil production had declined sharply from about 45 b./d. to 1 b./d. During the five-month period after surfactant injection was started, the well operated continuously except for five interruptions to bail sand. Sanding is normal in this well and not related to the surfactant treatment. During the test period, the well produced over 700 barrels of oil, and the surfactant cost was about 4/bbl. of incremental oil.

Kosanke well 75 normally produces oil (11 API, 42,000 cp. at 80 F.) and 75% water. This well was frequently shut down before the downhole emulsification test because either the rods would not drop or the pumping unit became overloaded. As a result, the well operated only about 66% of the time during the 12 months preceding the test. The well had been steamed about 12 months prior to the field test, and production had declined from about b./d. to about 12 b./d. Before the test, the pumping unit was limited to 8 s.p.m., and the annular fluid level was about 700 FOP. After the test was started, it was possible to replace the two-inch insert pump with a 2% inch tubing pump, increase pumping unit speed to 12 s.p.m., and pump off the well. During the six-month test the well operated continuously. The slope of the production decline curve was reduced, and the well produced over 600 bbl. additional oil. Surfactant cost was about 11'/bbl. of incremental oil.

Kosanke well 65A normally produces 30% oil (11 API, 42,000 cp. at 80 F.) and 70% Water. This well operated continuously before the test, but production was curtailed by lazy rods, which were floating at 8 s.p.m. The well had been steamed about 12 months before the test, and production had declined from about 50 b./d. to about 25 b./d. After surfactant injection was started, the pump was lowered 30 feet, the pumping unit was operable at 12 s.p.m., and annular fluid level was lowered from about 250 FOP to 0 FOP. After the well pumped ofl, pumping unit speed was lowered to 10 s.p.m. to avoid pounding. During the six-month test the slope of the decline curve was reduced, and the well produced over 400 barrels additional oil. Surfactant cost was about 29 per incremental barrel of oil. The mechanical changes of pump size, pump depth, and increased pumping unit speeds which permitted the Kosanke wells to take advantage of additional oil available from steam stimulation would not have been possible without downhole emulsification. The use of surfactant DM-7l0 in the three Kosanke wells did not interfere with the normal oilwater separating and cleaning procedures.

KCL 39 well 179 normally produces 15% oil, water. This well was frequently shut down for the same reasons as Kosanke 75 and was selected for testing a batch treatment process. The well has been batched treated twice. The first treatment was Sept. 25, 1967. Treatment consisted of dumping 2 gallons of DM-710 in 20 barrels fresh water down the casing-tube annulus and circulating the well before returning the well to production. Rod drop improvement lasted 5-6 days after each treatment. Surfactant cost was about 5/bbl. of oil.

The downhole emulsification tests in the Kern River Field have demonstrated that the proper use of nonionic surfactants can increase productivity and improve operating efficiency in any rod-pumped well in which productivity is limited by rod fall rate or high flow line pressure drop. In particular, downhole emulsification should be effective in extending the producing period in steamed wells where fluid is still available at the pump, but pump efficiency or pumping rate is limited by high oil viscosity. The result would be a reduction in steam stimulation frequency and increased production from each steam stimulation cycle.

While certain preferred embodiments of the invention have been specifically disclosed, it should be understood that the invention is not limited thereto as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims.

We claim:

1. In a method of pumping viscous crude from a well by a downhole pump in said well, the improvement of increasing the pumpability of said viscous crude which comprises injecting a nonionic surfactant into the well at a rate within the range of from .02 pound of surfactant per barrel of oil produced from the well and .4 pound of surfactant per barrel of oil produced from the well, contacting water and oil with said nonionic surfactant in said well to form an oil-in-water emulsion in said well and pumping said oil-in-water emulsion from said well.

2. The method of claim 1 where the surfactant is selected from the group consisting of:

3. The method of claim 1 further characterized in that the surfactant is injected into the well at a rate in the range of from .05 pound of surfactant per barrel of oil produced from said well and .15 pound of surfactant per barrel of oil produced from said well.

4. The method of claim 3 where the surfactant is selected from the group consisting of:

and

12 where R, R and R =any hydrocarbon group and n and 11 :4 to 100.

5. The method of claim 1 further characterized in that about .1 pound of surfactant per barrel of oil produced from the well is injected into the well.

6. The method of claim 5 where the surfactant is selected from the group consisting of:

where R, R and R =any hydrocarbon group and n and H124 to 100.

References Cited UNITED STATES PATENTS 2,874,779 2/1959 Johnson 166-42 3,196,947 7/1965 Van Poollen l6645 3,380,531 3/1968 McAuliffe et al. l66-45 ERNEST R. PURSER, Primary Examiner US. Cl. X.R. 252-8.55 

